Modern developments in telecommunications technology have lead to integrated services communications transmission and switching systems for narrow band and broadband communications services that have light waveguides in the region of the subscriber lines as a transmission medium The light waveguides provide both narrow band communications services such as, in particular, 64 kbit/s digital telephony as well as broadband communications services such as, in particular, 140 Mbit/s picture telephone. As a result narrow band signal switching matrix networks and broadband signals switching matrix networks (preferably having shared control equipment) can also be provided side-by-side in the switching centers (see German Patent 24 21 002 and corresponding U.S. Pat. No. 3,980,831).
A known broadband signal switching matrix network (see, for example, European Patent A1 0 262 477 and corresponding U.S. Pat. No. 4,801,936) has a cross-point matrix in FET technology whose s elements are each formed with a switching transistor that has its control electrode charged with a through-connect or inhibit signal and has its main electrode connected to the appertaining matrix output line. The switching elements each have a series transistor forming a series circuit with the switching transistor. This series transistor has its control electrode connected to the appertaining matrix input line and its main electrode connected opposite from the series circuit being connected via a sampling transistor to one terminal of an operating voltage source to whose other terminal the respective matrix output line is connected via a precharging transistor. The pre-charging transistor and sampling transistor are respectively charged oppositely from one another at their control electrode with a switching matrix network selection clock that subdivides a bit through-connect time span into a pre-charging phase and into the actual through-connection phase. As a result the matrix output line, for an inhibited sampling transistor, is at least approximately charged in every preliminary phase to the potential at the other terminal of the operating voltage source.
This known broadband signal switching matrix network that can have sampling transistors individually associated to the switching elements or sampling transistors, which are individually associated to the matrix input line or matrix output line, requires separate clock lines that run through the cross-point matrix for selecting these sampling transistors. This requires a circuit surface space requirement and involves a corresponding capacitative load on the matrix output lines. In order to guarantee adequate protection against signal interference, clock distribution and couplings between matrix input lines and matrix output lines require adequately high signal amplitudes on the matrix output lines, this involving a relatively high power consumption.